Grease a 9x13-inch or similar baking dish. Place the bread cubes in the baking dish.

In a large bowl, whisk together the eggs, milk, brown sugar, vanilla, cinnamon, nutmeg, and salt. Pour the mixture evenly over the bread. If making the casserole ahead, cover the baking dish and refrigerate overnight. Otherwise, let stand for 30 minutes at room temperature to allow the bread to soak up the egg mixture.

Preheat the oven to 350°F.

Add the topping: Drizzle the casserole with the butter and sprinkle with the brown sugar and pecans. Cover and bake for 35 minutes, then uncover and bake for another 10 to 20 minutes, or until the topping is browned and the egg mixture has mostly set. Remove from the oven, cover loosely with foil, and let stand for 10 minutes.

Serve with maple syrup.